Prior art includes a plurality of soil-working agricultural implements, whose working depth can be adjusted by means of hydraulic cylinders, which act between the frame of the agricultural implement and a support, such as a wheel or a packer roller.
A first type of soil-working agricultural implement is a so-called cultivator, which can be designed to be towed behind a towing vehicle, such as a tractor, and which can have a front wheel pair, followed by a plurality of rows of cultivating teeth or tines as well as, at the rear, a packer roller, or vice versa. Between on the one hand the frame and, on the other hand, the wheel pair and the packer roller, respectively, hydraulic cylinders are provided whose function is to set a distance between the respective frame portion and the ground, thereby controlling the working depth of the cultivating tines.
To provide a simple hydraulic system for such an agricultural implement, the hydraulic cylinders that control the packer roller and the hydraulic cylinders that control the wheel pair can be connected in parallel. By using hydraulic cylinders of different length of stroke and levers of different length, it is possible to obtain an agricultural implement, where the hydraulic cylinders of the packer roller and the wheel pair are connected in parallel and supplied via the same line, but where for example the packer roller is pulled up further than the wheel pair, such that the agricultural implement comes to rest on the wheel pair while the packer roller is lifted completely out of the soil.
The parallel coupling also offers the possibility of “self-adjustment”, since the amount of hydraulic fluid present in the system can flow between the hydraulic cylinders controlling the packer roller and the hydraulic cylinders controlling the wheel pair. This kind of self-adjustment makes it easier to handle soil irregularities, for example when towing the implement across soil portions that are concave or convex, as viewed from the side.
In use, a soil-working agricultural implement is usually towed in a substantially straight direction across the soil surface that is to be worked. When you arrive at the turn strip, the agricultural implement must be turned. Such a turn can be, for instance, approximately 90° or approximately 180°. Such turns would cause considerable stress on the tools of the agricultural implement and so it is desirable to lift them out of the soil before commencing the turn and then to lower them again once the turn has been completed.
A particular challenge in conjunction with systems connected in parallel is to have the agricultural implement, after the turn, return to the same working depth as before the turn.